The research proposed herein is designed to investigate some of the physiological determinants of aggressive behavior in hamsters and gerbils. Specifically, the contribution of gonadal steroids to sex differences in adult patterns of aggressive behavior will be investigated in hamsters and gerbils. Furthermore, an effort will be made to identify regions of the brain that are acted upon by gonadal hormones to influence aggressive behavior in each species. In hamsters, the possibility that androgen is converted to estrogen before influencing aggressive behavior will be investigated, and in female gerbils, the social and hormonal variables contributing to the display of sexual receptivity will be investigated.